The invention relates to a charger device connected to an accumulator and combined with a protection circuit for reverse polarity and overload protection, and a method of controlling the power supply device.
Patent specification DE 197 56 825 A1 describes a polarity reversal protection circuit with a switching element disposed between an input terminal and an output terminal, which does not allow a current flow unless the voltage at the input terminal is of a certain polarity. If a specific polarity is applied to the input terminal, the switching element connects through and if the polarity is not correct, it is opened or deactivated. The disadvantage of this system is that there is protection on the input side only.
An electronic circuit with polarity reversal protection is also known from patent specification DE 197 17 527 A1, in which a switching element, in particular a MOS field-effect transistor, is connected between an input source connected to a DC voltage source and a downstream circuit structure, and the switching element is activated if the DC voltage source is at the correct polarity and deactivated if the polarity is not correct. Again, the disadvantage of this approach is that there is protection on the input side only.
Patent specification DE 40 31 228 C1 discloses a circuit designed to protected against incorrect polarity, in which a field-effect transistor (FET) is disposed between a DC voltage supply source (Q) and a consumer (V) in the positive or negative line. The gate terminal of the field-effect transistor is always connected via a diode (D1) to the antipole or the line in which the field-effect transistor is not disposed. If a situation arises in which the polarity is not correct, a clearing current (IA) flows across the diode (D1), as a result of which the gate capacitance is discharged at the FET and the field-effect transistor is switched off with virtually no delay. Once the DC voltage source is correctly polarized again, the field-effect transistor is charged with the gate source capacitance again because the diode DI is now in the locked position so that the gate capacitance of the FET can be re-charged and the consumer current IV is able to flow across it again. The disadvantage of this solution is that the circuit design can be used to protect against incorrect polarity only and can not be used to provide other safety features.
The object of the invention is to provide a charger connected to an accumulator and a method of controlling the power supply, which will protect the power supply on the output side, such as a polarity reversal protection, an overload protection and/or a load detection system.
This object is achieved by the invention due to the fact that a control mode of a first switching element in the protection circuit is connected to another switching element to which a negative potential of the charger device can be switched, or to a control output of a control device of the charger device, and the control mode is also connected to a positive potential of a supply voltage source. The switched state of the first switching element is determined by the switched state of the other switching element. The advantage of this approach is that a circuit design of this type does not require a counter voltage to charge an accumulator, which enables fully discharged accumulators to be charged. Another advantage resides in the fact that not only can a charger device of this type be used to charge accumulators, it can also be used to supply energy for another consumer because other safety features can be run in addition to polarity reversal protection, such as overload protection and a load detection system, for example.
The object is also achieved by a method in which, when the charger device is connected to the power source, the first switching element for the polarity reversal protection is activated, even if the accumulator is not connected, and if the opposite (incorrect) polarity appears at the output terminals, another switching element is activated, as a result of which the voltage applied to a control node of the first switching element is applied to the negative potential, thereby switching off or deactivating the first switching element.
The invention will be explained in more detail with reference to presently preferred embodiments.